Temperature of a device may be regulated by a thermostat that controls flow of coolant from the device to a radiator or heat exchanger. Some example devices may include but are not limited to a fuel cell, engine, battery, motor, inverter, compressor, turbine, and amplifier. The thermostat is mechanically held closed when device temperature is less than a threshold temperature. The thermostat begins to open after device temperature is greater than the threshold temperature. Thermostat opening and closing is controlled via melting and solidification of wax material within the thermostat. Such systems may be sufficiently reliable; however, they may not regulate device temperature as tightly as is desired.
Another type of device temperature control system is described in U.S. Pat. No. 6,857,576 and it supplies heat to a wax material in a valve based on a temperature difference between an engine (e.g., the device) and a radiator. This system may improve engine temperature control as compared to a system that relies solely on melting of a wax material via engine coolant, but it also requires two temperature sensors and it may not respond as rapidly as is desired. Consequently, engine temperature control may not be as accurate as is desired.
The inventors herein have recognized the above-mentioned limitations and have developed a method for adjusting device temperature, comprising: adjusting an amount of electrical current supplied to a heater, the heater in thermal communication with a wax material in a valve, the amount of electrical current adjusted to one of two states, the amount of electrical current adjusted in response to a sign of a derivative of an output of a sole temperature sensor.
By adjusting heater current responsive to a derivative of device temperature, it may be possible to provide an accurate and fast response to changes in device temperature. In one example, heater current may switch between substantially zero current (e.g., less than 300 mA) and substantially rated heater current (e.g., within 500 mA of rated heater current) to control engine temperature. For example, when engine temperature is increasing and greater than a desired temperature, heater current can be rapidly increased to heat a wax medium that controls coolant flow through a valve. The heat causes the wax medium to change state and allows coolant to flow through the radiator from the engine, thereby providing cooling to the engine. Similarly, when engine temperature is decreasing and less than a desired temperature, heater current can be rapidly decreased to allow a wax medium that controls coolant flow through a valve to cool. The reduction in heat causes the wax medium to change state and limits coolant to flow through the radiator from the engine, thereby reducing cooling to the engine. In this way, a bang-bang controller that adjusts heater current to regulate coolant flow from an engine through a radiator may be provided to rapidly and accurately control engine temperature.
The present description may provide several advantages. In particular, the approach may improve engine temperature control. Further, the approach may reduce engine emissions, improve performance, and increase durability by more accurately controlling engine temperature. Additionally, the approach may provide improved temperature control while only relying on a single engine temperature sensor, if desired.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.